I think Buddhist tradition has a long established rule that "being absent of emotion/feeling, being robotic, etc." is not mushin - that it is a misunderstanding, a "beginner mistake," etc.

That said, it is still noted, rightly so, that much of our suffering is self-generated, by our attachment to things like self-identity, our pride, our fears, etc. So, while one is not expected to be "joyous" or "apathetic" at the passing of a child, for example, one is also supposed to realize that one's emotional responses are very often habitual in nature and thus part of the never-ending cycle of self-caused suffering.